There is a nice overview history of the Nashville Union & American newspaper on the Chronicling America.gov website that you will want to read. The paper contains much information that may be useful in your research – content can range widely from advertisements, state government proceedings, runaway slave notices, and more.

Combined with the already available issues of the Memphis Daily Appeal from 1857-1876 that makes for more than 6,000 issues of TN newspapers on the site. More will be added and we will share more news as we learn of it.